Optical fiber ribbons having a preferential separation sequence

ABSTRACT

A fiber optic ribbon having a predetermined separation sequence including a first subunit having a plurality of optical fibers arranged in a generally planar configuration being connected by a first primary matrix. The first subunit being a portion of a first ribbon-unit. A second subunit having a plurality of optical fibers arranged in a generally planar configuration being connected by a second primary matrix. The second subunit being a portion of a second ribbon-unit that includes a plurality of subunits. A secondary matrix connects the first ribbon-unit and the second ribbon-unit. The secondary matrix has a preferential tear portion disposed adjacent to a ribbon-unit interface defined between the first ribbon-unit and the second ribbon-unit.

RELATED APPLICATIONS

[0001] The present application is a Continuation-In-Part (CIP) of U.S.Ser. No. 10/159,730 filed on May 31, 2002, the disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates generally to fiber optic ribbons.More specifically, the invention relates to fiber optic ribbons having apreferential separation sequence for tearing the fiber optic ribbon.

BACKGROUND OF THE INVENTION

[0003] Fiber optic ribbons include optical waveguides such as opticalfibers that transmit optical signals, for example, voice, video, and/ordata information. Fiber optic cables using optical fiber ribbons canresult in a relatively high optical fiber-density. Fiber optic ribbonconfigurations can be generally classified into two general categories.Namely, fiber optic ribbons with subunits and those without. A fiberoptic ribbon with a subunit configuration, for example, includes atleast one optical fiber surrounded by a primary matrix forming a firstsubunit, and a second subunit having a similar construction, which arecontacted and/or encapsulated by a secondary matrix. On the other hand,fiber optic ribbons without subunits generally have a plurality ofoptical fibers surrounded by a single layer of matrix material.

[0004] Optical fiber ribbons should not be confused with micro-cablesthat, for example, have a strength member and a jacket. For instance,U.S. Pat. No. 5,673,352 discloses a micro-cable having a core structureand a jacket. The core structure requires that at least one opticalfiber is positioned between longitudinally extending strength members,both of which are embedded in a buffer material. The jacket protects thecore structure and the material is selected to have good adhesion to thebuffer material and be abrasion resistant. Additionally, the strengthmembers are required to have a larger diameter than the diameter of theoptical fiber, thereby absorbing crushing forces that are applied to thecable.

[0005] On the other hand, optical fiber ribbons generally have aplurality of adjacent optical fibers arranged in a generally planararray forming a relatively high optical fiber density. Optical fiberribbons without subunits can present problems for the craft. Forexample, when separating these optical fiber ribbons into optical fibersubsets, the craft must use expensive precision tools. Moreover,connectorization/splice procedures can require inventories ofspecialized splice and closure units/tools for the various subsets ofoptical fibers. Where the craft elects to separate the optical fiberribbon into subsets by hand, or with a tool lacking adequate precision,stray optical fibers and/or damage to the optical fibers can result.Stray optical fibers can cause problems in optical ribbonconnectorization, organization, stripping, and splicing. Additionally,damage to the optical fibers is undesirable and can render the opticalfiber inoperable for its intended purpose.

[0006] However, there are fiber optic ribbon configurations that attemptto aid the separation of fiber optic ribbons without using subunits. Forexample, U.S. Pat. No. 5,982,968 requires an optical fiber ribbon ofuniform thickness having V-shaped stress concentrations in the matrixmaterial that extend along the longitudinal axis of the fiber opticribbon. V-shaped stress concentrations can be located across from eachother on the planar surfaces of the fiber optic ribbon, thereby aidingthe separation of the fiber optic ribbon into subsets. However, the '968patent requires a wider fiber optic ribbon because additional matrixmaterial is required adjacent to the optical fibers near the V-shapedstress concentrations to avoid stray optical fibers after separation. Awider ribbon requires more matrix material and decreases the opticalfiber density. Another embodiment of the patent requires applying a thinlayer of a first matrix material around optical fibers to improvegeometry control such as planarity of the optical fibers. Then V-shapedstress concentrations are formed in a second matrix applied over thefirst matrix material, thereby allowing separation of the subsets at thestress concentrations.

[0007] Another example of a separable fiber optic ribbon is described inU.S. Pat. No. 5,970,196. More specifically, the '196 patent requires apair of removable sections positioned in V-shaped notches located acrossfrom each other on opposite sides of the planar surfaces of an opticalfiber ribbon. The removable sections are positioned between adjacentinterior optical fibers of the optical fiber ribbon to facilitate theseparation of the optical fiber ribbon into subsets at the V-shapednotches. The removable sections can either be flush with the planarsurfaces of the optical fiber ribbon, or they may protrude therefrom.These known fiber optic ribbons have several disadvantages. For example,they can be more expensive and difficult to manufacture. Additionally,from an operability standpoint, the V-shaped stress concentrationsand/or V-shaped notches can undesirably affect the robustness of theoptical fiber ribbon and/or induce microbending in the optical fibers.

[0008] Fiber optic ribbons that employ subunits to aid separationgenerally do not encounter these problems; however, they can have otherproblems. A conventional optical fiber ribbon 1 employing subunitsencapsulated in a secondary matrix is shown in FIG. 1. Optical fiberribbons having subunits can have several advantages, for example,improved separation, and avoidance of stray fiber occurrences. Inparticular, optical fiber ribbon 1 includes a pair of conventionalsubunits 2 having optical fibers 3 encapsulated in a primary matrix 5,which are then encapsulated in a secondary matrix 4. The thickness T1 ofprimary matrix 5 is continuous and uniform. Likewise, the thickness t1of the secondary matrix 4 covering the planar portions of subunits 2 iscontinuous and uniform. For example, subunit 2 can include six 250 μmoptical fibers 3 disposed in primary matrix 5 having an overall uniformthickness T1 of 310 μm and secondary matrix 4 has a thickness t1 of 10μm for an overall fiber optic ribbon thickness T2 of 330 μm.

[0009] However, conventional optical fiber ribbon 1 has disadvantages.For example, one concern is the potential formation of wings W (FIG. 1)during hand separation of subunits 2. Wings W can be cause by, forexample, a lack of sufficient adhesion between common matrix 4 andsubunit matrix 5 and/or random fracturing of the secondary matrix duringseparation. The existence of wings W can negatively affect, for example,optical ribbon organization, connectorization, stripping, and/orsplicing operations by the craft. Additionally, wings W can causeproblems with ribbon identification markings, or compatibility of thesubunit with ribbon handling tools, for example, thermal strippers,splice chucks, and fusion splicers.

SUMMARY OF THE INVENTION

[0010] The present invention is directed to a fiber optic ribbon havinga predetermined separation sequence including, a first subunit, a secondsubunit, and a secondary matrix. The first and second subunits each havea respective plurality of optical fibers arranged in a generally planarconfiguration being connected by respective first and second primarymatricies. The first subunit is a portion of a first ribbon-unit andsecond subunit is a portion of a second ribbon-unit that includes aplurality of subunits. The secondary matrix connects the firstribbon-unit and the second ribbon-unit so that the secondary matrix hasa preferential tear portion disposed adjacent to a ribbon-unit interfacedefined between the first ribbon-unit and the second ribbon-unit.

[0011] The present invention is also directed to a fiber optic ribbonhaving a predetermined separation sequence including a first subunit, asecond subunit, and a secondary matrix. The first and second subunitshave a respective plurality of optical fibers arranged in a generallyplanar configuration being connected by respective first and secondprimary matricies having a non-uniform thickness. The first subunit is aportion of a first ribbon-unit and the second subunit is a portion of asecond ribbon-unit that includes a plurality of subunits. A ribboninterface is formed between the first subunit and the second subunit andthe secondary matrix connects the first ribbon-unit and the secondribbon-unit. The secondary matrix has at least one local minimumthickness adjacent to the ribbon-unit interface so that the secondarymatrix fractures at the ribbon interface before fracturing at a subunitinterface of one of the ribbon-units.

[0012] The present invention is further directed to a fiber optic ribbonincluding a first subunit, a second subunit, and a secondary matrix. Thefirst and second subunits including respective pluralities of opticalfibers being contacted by respective first and second primary matricies.The first subunit is a portion of a first ribbon-unit and the secondsubunit is a portion of a second ribbon-unit having at least twosubunits. The first and second ribbon-units are generally aligned alonga plane. The secondary matrix has a cross-section with a non-uniformthickness that contacts portions of the first and second subunits. Thesecondary matrix also has at least one recessed portion defining atleast a portion of a preferential tear portion. The at least onerecessed portion being adjacent to a ribbon-unit interface definedbetween the first ribbon-unit the second ribbon-unit.

[0013] Additionally, the present invention is directed to a fiber opticribbon having a predetermined separation sequence including a firstsecondary matrix, a second secondary matrix, and a tertiary matrix. Thefirst secondary matrix connecting at least a first subunit and a secondsubunit together, thereby forming a first ribbon-unit, wherein the firstand second subunits respectively include a plurality of optical fibersarranged in a generally planar configuration being connected by arespective primary matrix. The second secondary matrix connecting atleast a third subunit and a fourth subunit together, thereby forming asecond ribbon-unit, wherein the third and fourth subunits respectivelyinclude a plurality of optical fibers arranged in a generally planarconfiguration being connected by a respective primary matricies. Thetertiary matrix connects the first ribbon-unit and the secondribbon-unit. The tertiary matrix has a preferential tear portion at aninterface between the first ribbon-unit and the second ribbon-unit.

BRIEF DESCRIPTION OF THE FIGURES

[0014]FIG. 1 is a cross-sectional view of a conventional optical fiberribbon according to the background of the present invention.

[0015]FIG. 2 is a cross-sectional view of a fiber optic ribbon accordingto one embodiment of the present invention.

[0016]FIG. 3 is a cross-sectional view of another fiber optic ribbonaccording to the present invention.

[0017]FIG. 3a is a partial cross-sectional view of other fiber opticribbons according to the present invention.

[0018]FIG. 4 is a cross-sectional view of the fiber optic ribbon subunitof FIG. 2 having a secondary matrix on portions thereof.

[0019]FIG. 5 is a cross-sectional view of another fiber optic ribbonaccording to the present invention.

[0020]FIG. 6 is a cross-sectional view of the fiber optic ribbon of FIG.5 after separation into subunits.

[0021]FIG. 7 is a cross-sectional view of another fiber optic ribbonaccording to the present invention.

[0022]FIG. 8 is a cross-sectional view of another fiber optic ribbonaccording to the present invention.

[0023]FIG. 9 is a cross-sectional view of another fiber optic ribbonaccording to the present invention.

[0024]FIG. 10 is a schematic, partial cross-sectional view of anotherfiber optic ribbon according to the present invention.

[0025]FIG. 11 is a cross-sectional view of a fiber optic ribbon having apreferential separation sequence according to the present invention.

[0026]FIG. 12 is a cross-sectional view of another fiber optic ribbonhaving a preferential separation sequence according to the presentinvention.

[0027]FIG. 13 is a cross-sectional view of a fiber optic ribbon having apreferential separation sequence according to the present invention.

[0028]FIG. 14 is a cross-sectional view of a fiber optic cable accordingto the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0029] Illustrated in FIG. 2 is a fiber optic ribbon 10 according to thepresent invention. Fiber optic ribbon 10 (hereinafter ribbon) includes aplurality of optical waveguides, for example, optical fibers 12 arrangedin a generally planar configuration with a primary matrix 14 forming anelongate structure. Ribbon 10 can, for example, be used as a stand-aloneribbon, a portion of a ribbon stack, or as a subunit of a ribbon.Primary matrix 14 generally contacts optical fibers 12 and mayencapsulate the same, thereby providing a robust structure forprocessing and handling. Primary matrix 14 generally fixes adjacentoptical fibers together in an elongate structure, thereby inhibitingrelative movement therebetween. Primary matrix 14 includes a first end14 a, a medial portion 14 b, and a second end 14 c. Additionally,primary matrix 14 has a cross-section having a non-uniform thickness.

[0030] In this embodiment, first end portion 14 a has a thickness T_(a)and second end portion 14 c has a thickness T_(c), which are bothgreater than a thickness T_(b) of medial portion 14 b. For example,thickness T_(a) is about 5 μm or greater than thickness T_(b); however,other suitable dimensions can be used. More particularly, first andsecond end portions 14 a, 14 c both have a generally bulbous shape;however, other suitable shapes can be used such as angular orelliptical. As used herein, bulbous shape means that an end portion ofthe ribbon has a thickness that is greater than the largest thickness ofa medial portion of the ribbon. Preferably, the largest thickness isgenerally adjacent to edge fiber 12 a, generally at a range r of aboutone-half to about one optical fiber diameter from the edge of thematrix, however, other suitable ranges can be used. Suitable values ofrange r generally dispose the largest thickness T_(a) over across-section of edge fiber 12 a. In other words, range r is between apoint tangent to a circumference of the edge fiber 12 a (shown by dashedline on left ribbon of FIG. 3A) to a point over edge fiber 12 a (shownby right ribbon of FIG. 3A) up to about one optical fiber diameter ormore inward from the edge of the matrix.

[0031] The present invention should not be confused with conventionalribbons having undulations across their cross-sections surfaces due tomanufacturing variances. These undulations can cause variations in theconventional ribbon thickness at random locations, rather than, forexample, predetermined shapes. For example, the thickness of theconventional ribbon can be 310±3 μm at random locations across thecross-section. On the other hand, ribbons according to the presentinvention can have, for example, a non-uniform thickness that increasesor decreases at predetermined locations to aid separation performance.

[0032] In one embodiment, optical fibers 12 are a plurality ofsingle-mode optical fibers; however, other types or configurations ofoptical fibers can be used. For example, optical fibers 12 can bemulti-mode, pure-mode, erbium doped, polarization-maintaining fiber,other suitable types of light waveguides, and/or combinations thereof.For instance, each optical fiber 12 can include a silica-based core thatis operative to transmit light and is surrounded by a silica-basedcladding having a lower index of refraction than the core. Additionally,one or more coatings can be applied to optical fiber 12. For example, asoft primary coating surrounds the cladding, and a relatively rigidsecondary coating surrounds the primary coating. The coating can alsoinclude an identifying means such as ink or other suitable indicia foridentification and/or an anti-adhesion agent that inhibits the removalof the identifying means. However, optical fibers used in ribbons of thepresent invention generally are not tight-buffered. Suitable opticalfibers are commercially available from Corning Incorporated of Corning,N.Y.

[0033] Primary matrix 14 can be, for example, a radiation curablematerial or a polymeric material; however, other suitable materials canbe used. As known to one skilled in the art, radiation curable materialsundergo a transition from a liquid to a solid when irradiated withpredetermined radiation wavelengths. Before curing, the radiationcurable material includes a mixture of formulations of, for example,liquid monomers, oligomer “backbones” with acrylate functional groups,photoinitiators, and other additives. Typical photoinitiators functionby: absorbing energy radiated by the radiation source; fragmenting intoreactive species; and then initiating a polymerization/hardeningreaction of the monomers and oligomers. Generally, as a result ofirradiation, a cured solid network of cross-linking is formed betweenthe monomers and oligomers, which may include fugitive components.Stated another way, the photoinitiator begins a chemical reaction thatpromotes the solidification of the liquid matrix into a generally solidfilm having modulus characteristics.

[0034] One aspect of the curing process is the reaction of aphotoinitiator in response to radiation exposure. A photoinitiator hasan inherent absorption spectrum that is measured in terms of absorbanceas a function of radiation wavelength. Each photoinitiator has acharacteristic photoactive region, i.e., a photoactive wavelength rangetypically measured in nanometers (nm). For example, commerciallyavailable photoinitiators can have a photoactive wavelength range in thevacuum ultra-violet (160-220 nm), ultra-violet (220-400 nm), or visiblelight (400-700 nm) wavelength ranges.

[0035] The resulting modulus of radiation curable materials can becontrolled by factors such as radiation intensity and cure time. Theradiation dose, i.e., the radiant energy arriving at a surface per unitarea is inversely proportional to the line speed, i.e., the speed theradiation curable moves past the radiation source. The light dose is theintegral of radiated power as a function of time. In other words, allelse being equal, the faster the line speed, the higher the radiationintensity must be to achieve adequate curing. After a radiation curablematerial has been fully irradiated, the material is said to be cured.Curing occurs in the radiation curable material from the side facing theradiation source down or away from the source. Because portions of thematerial closer to the radiation source can block radiation fromreaching non-cured portions of the material, a cure gradient can beestablished. Depending on the amount of incident radiation, a curedmaterial may exhibit different degrees of curing. Moreover, the degreesof curing in a material can have distinct modulus characteristicassociated therewith. Conversely, radiation sources can be positioned sothat the material has a relatively uniform cure.

[0036] Thus, the degree of cure affects the mechanical characteristicsthrough the cross-link density of the radiation curable material. Forexample, a significantly cured material can be defined as one with ahigh cross-link density for that material, which is, for example, toobrittle. Further, an undercured material may be defined as one having alow cross-link density, and can be too soft, possibly having arelatively high coefficient of friction (COF) that causes an undesirablelevel of ribbon friction. The cured UV material has a modulus, forexample, in the range of about 50 MPa to about 1500 MPa depending on theradiation dose. Different modulus values can provide varying degrees ofperformance with respect to, for example, hand separability androbustness of the ribbons of the present invention.

[0037] In one embodiment, a UV curable material is used for primarymatrix 14. For example, the UV curable material is a polyurethaneacrylate resin commercially available from DSM Desotech Inc. of ElginIll. such as 950-706. Alternatively, other suitable UV materials can beused, for example, polyester acrylate resin commercially available fromBorden Chemical, Inc. of Columbus, Ohio. Additionally, thermoplasticmaterials such as polypropylene can be used as a matrix material.

[0038]FIG. 3 illustrates a ribbon 20 another embodiment of the presentinvention that is similar to ribbon 10. Ribbon 20 includes a pluralityof optical waveguides, for example, optical fibers 12 arranged in agenerally planar configuration with a primary matrix 24 forming anelongate structure. Primary matrix 24 generally contacts optical fibers12 and may encapsulate the same, thereby providing a robust structurefor processing and handling. Primary matrix 24 includes a cross-sectionhaving a non-uniform thickness having a first end 24 a, a medial portion24 b, and a second end 24 c. In this embodiment, first end portion 24 ahas a thickness T_(a) and second end portion 24 c has a thickness T_(c),wherein thickness T_(a) is greater than a thickness T_(b) of medialportion 24 b. More particularly, first end portion 24 a, for example,has a generally bulbous shape; however, other suitable shapes can beused. Whereas, second end portion 24 c can have a shape that isgenerally different than the shape of first end portion 24 a. Forexample, as depicted, second end portion 24 c has a generally roundshape, however, other suitable shapes can be used such as flat, angled,radiused, or combinations thereof. When stacking a plurality of ribbonssimilar to ribbon 20, first end portion 24 a can be placed onalternating sides of the ribbon stack to provide stack integrity.Additionally, stacking ribbons in this manner still allows the ribbonsto move in at least two degrees of freedom when acted upon by forces,which can preserve optical performance.

[0039]FIG. 3a depicts a plurality of ribbons 30 having a primary matrix34 with a non-uniform cross-sectional thickness having thickness T_(a)disposed over a cross-section of the edge optical fiber. Specifically,an end portions 34 a is formed from several shapes such as linear andradius portions, thereby forming a generally angular end portion that isbulbous. Preferably, a medial portion 34 b has a thickness T_(b) thatextends over, or past, a diameter D of edge optical fiber 12 a. Byextending thickness T_(b) over, or past, diameter D of edge opticalfiber 12 a the planarity of the optical fibers of ribbon 30,particularly edge optical fiber 12 a, is easier to control.Additionally, end portion 34 a includes a predetermined angle α that caninfluence the amount of secondary matrix disposed between adjacentribbons 30 when they are used as subunits for larger ribbons. In otherwords, angle α can influence performance parameters such as twistperformance and separation characteristics when ribbons 30 are used assubunits by tailoring the amount of secondary matrix therebetween.Additionally, other suitable shapes can be used.

[0040]FIG. 4 depicts a ribbon 40. Ribbon 40 includes ribbon 10 with asecondary matrix 45 disposed on outwardly portions of primary matrix 14.Using more than one can have several advantages. For example, in oneembodiment a thin primary matrix can be applied to ensure planarity ofthe optical fibers in the ribbon. Additionally, secondary matrix 45 canhave several functions. For example, secondary matrix 45 can be usedimpart generally planar surfaces 46 to ribbon 40. Planar surfaces 46 canalso provide stability when ribbon 40 is used as a portion of a ribbonstack. Additionally, secondary matrix 45 may also provide materialcharacteristics that are different from primary matrix 14 such asadhesion, COF characteristics, or hardness. This can be accomplished,for example, by using a secondary matrix 45 material that is similar toprimary matrix 14 with different processing characteristics such as curecharacteristics, or by using a material that is different than primarymatrix 14. Likewise, different portions of secondary matrix 45 can bedifferent materials and/or have distinct material characteristics.

[0041] Illustratively, a first planar surface of secondary matrix 45 canhave a predetermined COF, while the second planar surface can have ahigh adhesion to primary matrix 14. A predetermined COF on the planarsurface allows the ribbon to relieve strain, for example, during bendingof a stack of ribbons. While a high adhesion characteristic between theprimary and secondary matrices can make for a generally robust ribbon.In other embodiments, the first and second planar surfaces can have thesame characteristics, which may differ from the characteristics of theprimary matrix. Additionally, as disclosed in U.S. Pat. No. 6,253,013,which is incorporated in its entirety herein by reference, an adhesionzone 44 (FIG. 4) can be used between primary matrix 14 and secondarymatrix 45. For example, adhesion zone 44 is applied to primary matrix 14using a Corona discharge treatment. Additionally, a marking indicia foridentifying ribbon 40 can be printed either on primary matrix 14 orsecondary matrix 45. In other embodiments, secondary matrix 45 can beused to identify ribbon 40. For example, secondary matrix 45 can becolored with a dye for identification of the ribbon.

[0042] Likewise, other suitable color combinations are possible foridentifying individual ribbons. In one embodiment, primary matrix 14 maybe a first color and secondary matrix 45 a second color. For example,multiple ribbons of a ribbon stack can have the same color primarymatrix with each different ribbon have a secondary matrix with adifferent color. Thus, the craftsman could identify the stack as theblue stack and each individual ribbon within the blue stack. In otherembodiments, the secondary matrix of the ribbons of the stack can be thesame color, with the primary matrix of the individual ribbon havingdifferent colors. Thus, each ribbon can be identified from the side ofthe stack. In still other embodiments, the primary or secondary matrixcan have stripes, or tracers, of suitable colors for use as identifyingindicia.

[0043]FIG. 5 depicts ribbon 50 another embodiment according to thepresent invention. Ribbon 50 includes two ribbons such as ribbons 10 foruse as a first subunit 51 and a second subunit 52. As used herein,subunit means a plurality of optical fibers having a discrete matrixmaterial thereon. In other words, each subunit has its own individualmatrix material thereon. Subunits should not be confused with subsets,which are optical fibers arranged as groups having a common matrixmaterial. When subunits are separated, the discrete matrix materialgenerally remains intact on each subunit. However, ribbons according tothe present invention can use other suitable types or numbers of ribbonsas subunits.

[0044] A secondary matrix 55 contacts portions of subunits 51, 52 and isgenerally dimensioned to provide a pair of opposing generally flatplanar surfaces 56. Secondary matrix 55 can have materialcharacteristics that are similar or different than the primary matrix.For example, the primary and/or the secondary matrix around the edgefibers of subunits 51, 52 can be relatively soft to cushion the same andinhibit optical attenuation therein. The generally flat planar surfaces56 allow ribbon 50 to be easily stacked to form a portion of a ribbonstack. However, other suitable shapes of secondary matrix 55 can beused. Using secondary matrix 55 allows separation of ribbon 50 at theinterface 57 between the subunits 51, 52 by, for example, hand. Subunits51, 52 preferably have a point of contact at interface 57, therebyallowing secondary matrix 55 to flow between the subunits and forming arobust structure. However, the subunits can be spaced apart at theinterface therebetween.

[0045] Additionally, ribbon 50 advantageously inhibits the formation of,for example, wings and/or stray optical fibers during separation. Ribbon50 inhibits the formation of wings by having a preferential tear portion58 in secondary matrix 55, rather than allowing random fracturing insecondary matrix 55. Specifically, preferential tear portion 58 isgenerally located at a point of local minimum thickness t2 (FIG. 6) andis generally adjacent to interface 57 of secondary matrix. In this case,the local minimum thickness t2 is formed by subunits 51, 52 havingnon-uniform cross-sections. When secondary matrix 55 with generally flatplanar surfaces 56 is applied over these non-uniform cross-sections, thethickness of secondary matrix 55 varies. For example, local minimumthickness t2 is about 2 μm, whereas portions of the secondary matrix 55over the medial portions of subunits 51, 52 have a thickness of about 10μm. In other embodiments, local minimum thickness t2 can approach avalue of essentially zero. Local minimum thickness t2 is a weak point,thereby allowing the fracture of secondary matrix 55 to begin and/orterminate at this point. Additionally, the minimum thickness can haveother suitable dimensions or locations, but should allow the ribbon tohave a suitable robustness and handleability. FIG. 6 illustrates theribbon 50 after separation by hand into subunits. As depicted, formationof wings is inhibited according to the concepts of the presentinvention. Additionally, using suitable matrix characteristics such aselongation to break and/or a predetermined matrix modulus can enhancethe preferential tear portion.

[0046] As depicted in FIG. 7, preferential tear portion can beaccomplished with other suitable ribbon geometries. Ribbon 70 includestwo subunits 71, 72 and a secondary matrix 75. Secondary matrix 75contacts and/or encapsulates subunits 71, 72 thereby forming ribbon 70.Like secondary matrix 55 of ribbon 50, secondary matrix 75 has athickness that varies generally adjacent to interface 77 betweensubunits 71, 72. However, the varying thickness of secondary matrix 75adjacent interface 77 is accomplished with subunits 71, 72 having agenerally uniform thickness. However, this ribbon configuration can beused in combination with subunits having a non-uniform thickness. In oneembodiment, secondary matrix 75 has a recessed portion having a width w,for example, the recessed portion defining a concave portion 73generally centered over interface 77. In other words, recessed portionsare generally symmetrical about an interface axis A-A that passesthrough interface 77 and is generally perpendicular to the generallyplanar surfaces of ribbon 70. However, in other embodiments, therecessed portion can have other shapes such as indentation 74, widths,and/or locations. For purposes of illustration, the top and bottom ofribbon 70 have different configurations of the recessed portion;however, embodiments can have the same shaped recessed portions 73 oneach side of interface 77. Concave portions 73 form a local minimumthickness in secondary matrix 75, which is a weak point thatadvantageously allows the fracture of secondary matrix 75 to beginand/or terminate at this point during, for example, hand separation.

[0047] In one embodiment, recessed portion 73 has a width w less thanabout 600 μm and a depth D of about 5 μm. However., other suitabledimensions can be used, for example, in other embodiments width w can beabout 200 μm or greater and depth D can be about 5 μm or greater.Furthermore, the recessed portions 73 of the ribbon should bedimensioned to provide suitable robustness and handleability for theintended application of the ribbon.

[0048] Ribbon 80, another embodiment according to the concepts of thepresent invention, is illustrated in FIG. 8. Ribbon 80 includes a pairof subunits 81, 82, each having a generally uniform thickness, and asecondary matrix 85 generally contacting and/or encapsulating subunits81, 82, thereby forming ribbon 80. Ribbon 80 has at least one recessedportion 83 and is similar to ribbon 70; however, recessed portions 83are centered over an interface 87 between subunits 81, 82. In thisembodiment, recessed portions 83 have a generally concave shape that isoffset at a distance d from interface 87. For example, distance d isbetween about 125 μm and about 300 μm, but other suitable distances canbe used. Additionally, recessed portions 83 can have other shapes,widths, and/or depths. For purposes of illustration, the top and bottomof ribbon 80 have a different number of recessed portions 83. Forexample, recessed portions 83 on the top of ribbon 80 are generallysymmetrical about interface axis A-A. However, other embodiments canhave the same, or different, number of recessed portions 83 on eachgenerally planar surface 86, for example, one, two, or more. Concaveportions 83 form a local minimum thickness in secondary matrix 85, whichis a weak point that advantageously allows the fracture of secondarymatrix 75 to begin and/or terminate at this point during, for example,hand separation, thereby inhibiting the formation of wings.

[0049] Recessed portions 83 should be dimensioned to provide suitablerobustness and handleability for the intended application of the ribbon.In this embodiment, centering recessed portions 83 of ribbon 80 atdistance d from interface 87 provides increased robustness to ribbon 80.Specifically, centering recessed portions 83 from interface 87 improvesthe twist performance of ribbon 80. For example, subunits 81, 82 ofribbon 80 are less likely to separate during normal handling of theribbon.

[0050]FIG. 9 illustrates a ribbon 90 that is another embodiment of thepresent invention that is similar to ribbon 50. Ribbon 90 includessubunits 91, 92 and a secondary matrix 95. Secondary matrix 95 contactsand/or encapsulates subunits 91, 92 thereby forming ribbon 90. Subunits91, 92 have a non-uniform thickness and secondary matrix 95 has aplurality of recessed portions, like ribbon 70. In this embodiment,recessed portions 83 are on both sides of interface axis A-A and aregenerally symmetrical thereabout. The recessed portions are defined as aplurality of concave portions 93; however, recessed portions can haveother shapes, widths, and/or locations. Concave portions 93 aregenerally located at a distance d from the interface of subunits 91, 92.In this embodiment, distance d locates the center of concave portions 93slightly beyond the largest thickness of the ends towards the medialportions of the subunits 91, 92.

[0051]FIG. 10 illustrates a portion of ribbon 100, which is anotherembodiment that is similar to ribbon 90. Ribbon 100 includes subunits101, 102 and a secondary matrix 105. Subunits 101, 102 have anon-uniform thickness and secondary matrix 105 has plurality of recessedportions that are symmetrical about interface axis A-A, thereby forminga local minimum thickness t2. In this embodiment, local minimumthickness t2 is formed by having a radius R₁ of the subunit being lessthan an adjacent radius R₂ of the primary matrix, thereby forming apreferential tear portion. For example, local minimum thickness t2 canhave a range of about zero to about 5 μm; however, any other suitabledimension can be used. Radii R₁ and R₂ are generally located adjacent tolocal minimum thickness t2. Configuring the ribbon so that R₂ is greaterthan R₁, is intended to allow secondary matrix 105 material to generallyflow away from local minimum thickness t2 before curing or hardening ofthe same. In other words, radius R₁ and the surface tension of secondarymatrix 105 cause matrix 105 to flow away, thereby forming the localminimum thickness, rather than having primary matrix material flowtowards, and building-up the thickness of local minimum thickness t2.Additionally, other embodiments can also use this concept.

[0052]FIG. 11 illustrates ribbon 110 including a secondary matrix 115having a plurality of preferential tear portions 115 a, 115 b forseparating a plurality of ribbon-units A, B, and C, thereby providingribbon 110 with a preferential separation sequence. In other words,ribbon 110 has a preference to separate at a ribbon-unit interface(s)A/B and/or B/C before separating at a subunit interface such as betweensubunits 112, 113. In this embodiment, each subunit 111-114 includes twooptical fibers 12 that are connected by respective primary matrcies (notnumbered) having a generally uniform thickness. Each ribbon-unit A, B,and C includes at least one subunit, but at least one of theribbon-units should include at least two subunits. In this case,ribbon-unit B includes two subunits 112, 113 having two optical fibersand ribbon-units A and C each include one subunit having two opticalfibers. The preferential separation sequence occurs at the ribbon-unitinterfaces A/B and/or B/C because the preferential tear portions 115 a,115 b of secondary matrix 115 are disposed adjacent to respectiveribbon-unit interfaces. On the other hand, secondary matrix 115 has agenerally uniform thickness adjacent to the subunit interface betweensubunits 112, 113, thereby creating a more robust connection between thesubunit interface compared with the ribbon-unit interface. Preferentialtear portions 115 a are recessed portions and preferential tear portion115 b is an indentation. However, ribbons of the present invention caninclude any suitable preferential tear portion or feature to provide thepreferential separation sequence of the ribbon-units. For instance,other embodiments of ribbon 110 can have asymmetrical forms such as tworibbon-units A and B respectively having one and two subunits with aminimum of six optical fibers in the ribbon. Additionally, ribbon-unitscan include other suitable numbers of subunits and/or subunits caninclude suitable numbers of optical fibers.

[0053] Furthermore, the concepts of a preferential separation sequencebetween ribbon-units can employ subunits having other suitable geometry.For instance, FIG. 12 depicts ribbon 120 having ribbon-units E, F, Gwith respective subunits that can include a non-uniform thicknessconnected by a secondary matrix 127 having preferential tear portions.In this case, subunits 122-126 have at least a first end portion with athickness that is greater than a medial portion and subunit 121 is asubunit with a generally uniform thickness. Preferably, a first and asecond end of subunits are generally symmetrical so that orientationduring ribbonizing is of no concern; however, end portions can havedifferent shapes so that orientation during ribbonizing matters.Moreover, having generally symmetrical subunits with non-uniformthicknesses can inhibit the formation of wings during separation ofsubunits in the same ribbon-unit if necessary. As depicted, subunits122, 123, 124 have at least one end portions with a generally angularshape and subunits 124, 125, 126 have at least one end portions with agenerally bulbous shape.

[0054] As shown, secondary matrix 127 includes at least one preferentialtear portion disposed adjacent to ribbon interfaces E/F and F/G.Specifically, preferential tear portions of secondary matrix arerecessed portions 127 a having a generally concave shape that is offsetat a distance d from the ribbon-unit interface. For example, distance dis between about 125 μm and about 300 μm, but other suitable distancescan be used. Additionally, recessed portions 127 a can have othershapes, widths, and/or depths. Additionally, the top and bottom ofribbon 120 can have different numbers or shapes of recessed portions 127a. In this case, recessed portions 127 a are generally symmetrical aboutaxis A-A at the ribbon-unit interface.

[0055] Still further, the concepts of a preferential separation sequencebetween ribbon-units can employ more than two matrices. For instance,FIG. 13 depicts ribbon 130 having ribbon-units H, I, J connected by atertiatry matrix having preferential tear portions. Specifically, thesubunits of ribbon 130 include optical fibers connected by respectiveprimary matricies (not numbered) and each ribbon-unit H, I, J includestwo subunits connected by a respective secondary matrix 137 that areconnected by a tertiary matrix 138. Tertiary matrix 138 includespreferential tear portions such as recesses 138 a or indentations;however, any suitable preferential tear portion as described herein canbe used. Additionally, any of the matrices can include the materialcharacteristics, properties and/or features as discussed herein.

[0056] Moreover, the ribbons of the present invention can be used in anysuitable fiber optic cable design. FIG. 14 depicts a representativefiber optic cable 140 according to the present invention. Fiber opticcable 140 includes a stack 142 of ribbons 110 disposed in a tube 144having a sheath 146 therearound. Sheath 146 includes strength members146 a and a jacket 146 b. Although a monotube fiber optic cable designis depicted, the present invention can include the ribbons of thepresent invention in any suitable cable design such as dry-tube, slottedcore, drop cables, figure-eight, loose tube, or interconnect cables.Moreover, fiber optic cable 140, or any other cable configuration, caninclude more, or fewer, cables components such as ripcords, armorlayers, binder layers, strength members, tubeless, water-swellablecomponents, water-blocking materials, or any other suitable cablecomponents.

[0057] Many modifications and other embodiments of the presentinvention, within the scope of the appended claims, will become apparentto a skilled artisan. For example, subunits can include differentnumbers of optical fibers, ribbons can have more than two subunits, orthe ribbons can have other suitable configurations. Additionally,ribbons of the present invention can have suitable components such asripcords. Therefore, it is to be understood that the invention is not tobe limited to the specific embodiments disclosed herein and thatmodifications and other embodiments may be made within the scope of theappended claims. Although specific terms are employed herein, they areused in a generic and descriptive sense only and not for purposes oflimitation. The invention has been described with reference tosilica-based optical fibers, but the inventive concepts of the presentinvention are applicable to other suitable optical waveguides as well.

1-54. (canceled)
 55. A fiber optic ribbon, comprising: a first subunit,the first subunit having a first plurality of optical fibers arranged ina generally planar configuration being connected by a first primarymatrix, the first primary matrix having a first end portion and a medialportion, the first end portion having a generally bulbous shape, thegenerally bulbous shape having a thickness, and the medial portionhaving a thickness, wherein the thickness of the first end portion isgreater than the thickness of the medial portion; a second subunit, thesecond subunit having a second plurality of optical fibers arranged in agenerally planar configuration being connected by a second primarymatrix; a third subunit, the third subunit having a third plurality ofoptical fibers arranged in a generally planar configuration beingconnected by a third primary matrix, wherein the first subunit, thesecond subunit, and the third subunit all have equal numbers of opticalfibers; and a secondary matrix, the secondary matrix connecting thefirst subunit, the second subunit and the third subunit.
 56. The fiberoptic ribbon of claim 55, wherein the first subunit, the second subunit,and the third subunit all have four optical fibers.
 57. The fiber opticribbon of claim 55, the primary matrix of the second subunit having afirst end portion and a medial portion, the first end portion having agenerally bulbous shape, the generally bulbous shape having a thickness,and the medial portion having a thickness, wherein the thickness of thefirst end portion is greater than the thickness of the medial portion.58. The fiber optic ribbon of claim 55, the generally bulbous shapebeing disposed about an edge optical fiber of the first subunit.
 59. Thefiber optic ribbon of claim 55, the primary matrix of the first subunithaving a second end portion having a thickness, the thickness of thesecond end portion being greater than the thickness of the medialportion.
 60. The fiber optic ribbon of claim 55, the thickness of thefirst end portion being about Sum or greater than the thickness of themedial portion.
 61. The fiber optic ribbon of claim 55, the first andsecond subunits having a non-uniform thickness.
 62. The fiber opticribbon of claim 55, the primary matrix of the first subunit having apredetermined modulus and the secondary matrix having a predeterminedmodulus, wherein the modulus of the primary matrix has a different valuethan the modulus of the secondary matrix.
 63. The fiber optic ribbon ofclaim 55, the primary matrix of the first subunit having at least onepredetermined material characteristic and the secondary matrix having atleast one predetermined material characteristic, the at least onepredetermined material characteristic of the primary matrix having adifferent value than the at least one predetermined materialcharacteristic of the secondary matrix.
 64. The fiber optic ribbon ofclaim 55, the secondary matrix having at least one local minimumthickness, the at least one local minimum thickness being adjacent to aninterface between subunits.
 65. The fiber optic ribbon of claim 64, theat least one local minimum thickness being in the range of about zero toabout 5 μm.
 66. The fiber optic ribbon of claim 55, the fiber opticribbon being a portion of a fiber optic cable.
 67. A fiber optic ribbon,comprising: a first subunit, the first subunit having a plurality ofoptical fibers arranged in a generally planar configuration beingconnected by a first primary matrix having a non-uniform thickness; asecond subunit, the second subunit having a plurality of optical fibersarranged in a generally planar configuration being connected by a secondprimary matrix having a non-uniform thickness; a third subunit, thethird subunit having a plurality of optical fibers arranged in agenerally planar configuration being connected by a third primary matrixhaving a non-uniform thickness; and a secondary matrix, the secondarymatrix connecting the first subunit, the second subunit, and the thirdsubunit.
 68. The fiber optic ribbon of claim 67, wherein the firstsubunit, the second subunit, and the third subunit all have four opticalfibers.
 69. The fiber optic ribbon of claim 67, the primary matrix ofthe first subunit having a first end portion and a medial portion, thefirst end portion having a generally bulbous shape, the generallybulbous shape having a thickness, and the medial portion having athickness, wherein the thickness of the first end portion is greaterthan the thickness of the medial portion.
 70. The fiber optic ribbon ofclaim 69, the primary matrix of the first subunit having a second endportion having a thickness, the thickness of the second end portionbeing greater than the thickness of the medial portion.
 71. The fiberoptic ribbon of claim 69, the thickness of the first end portion beingabout 5 μm or greater than the thickness of the medial portion.
 72. Thefiber optic ribbon of claim 69, the primary matrix of the second subunithaving a first end portion and a medial portion, the first end portionhaving a generally bulbous shape, the generally bulbous shape having athickness, and the medial portion having a thickness, wherein thethickness of the first end portion is greater than the thickness of themedial portion.
 73. The fiber optic ribbon of claim 67, the firstsubunit having a generally bulbous shape being disposed about an edgeoptical fiber of the first subunit.
 74. The fiber optic ribbon of claim67, the primary matrix of the first subunit having a predeterminedmodulus and the secondary matrix having a predetermined modulus, whereinthe modulus of the primary matrix has a different value than the modulusof the secondary matrix.
 75. The fiber optic ribbon of claim 67, theprimary matrix of the first subunit having at least one predeterminedmaterial characteristic and the secondary matrix having at least onepredetermined material characteristic, the at least one predeterminedmaterial characteristic of the primary matrix having a different valuethan the at least one predetermined material characteristic of thesecondary matrix.
 76. The fiber optic ribbon of claim 67, the secondarymatrix having at least one local minimum thickness being in the range ofabout zero to about 5 μm.
 77. The fiber optic ribbon of claim 67, thefiber optic ribbon being a portion of a fiber optic cable.
 78. A fiberoptic ribbon, comprising: a first subunit, the first subunit including afirst plurality of optical fibers, the first plurality of optical fibersbeing contacted by a first primary matrix; a second subunit, the secondsubunit including a second plurality of optical fibers, the secondplurality of optical fibers being contacted by a second primary matrix;a third subunit, the third subunit including a third plurality ofoptical fibers, the third plurality of optical fibers being contacted bya third primary matrix, wherein the first, second, and third subunitsall have an equal number of optical fibers; and a secondary matrixconnecting the first subunit, the second subunit, and the third subunit.79. The fiber optic ribbon of claim 78, the first subunit having across-section with a non-uniform thickness.
 80. The fiber optic ribbonof claim 78, the first subunit having a generally bulbous shape beingdisposed about an edge optical fiber of the first subunit.
 81. The fiberoptic ribbon of claim 78, the first subunit having a first end portionhaving a predetermined thickness and a medial portion having apredetermined thickness, wherein the thickness of the first end portionis greater than the thickness of the medial portion.
 82. The fiber opticribbon of claim 78, the fiber optic ribbon being a portion of a fiberoptic cable.
 83. The fiber optic ribbon of claim 78, the secondarymatrix having a cross-section with a non-uniform thickness, wherein thesecondary matrix has at least one recessed portion defining at least aportion of a preferential tear portion, the at least one recessedportion being adjacent to an interface between two of the subunits.